PART 4 – BLOWERS: REGENERATIVE, POSITIVE DISPLACEMENT, ROTARY VANE, AND TURBO FANS.
Selecting the right blower for your application can be difficult because there are a lot of different kinds of blowers that may meet your pressure and flow specification. So how do you know which one to choose? Which brand is right for my application?
First we will talk about the general differences between the regenerative, positive displacement (PD), rotary vane and fan type blowers. The simplest way to explain the differences is by flow and pressure and then by other factors such as noise, heat, power draw and durability. The highest flow in SCFM is usually generated by fan blowers (or turbo fans) followed by regenerative blowers, PD blowers and rotary vanes.
The highest pressure (positive or negative) is usually generated by the rotary vane blowers, followed by the PD blowers, regenerative blowers and fans. So as you can guess, if you want a blower with high flow and high vacuum several unit types may overlap with their specifications. The next thing to consider is how much flow and pressure can I get per horsepower required for the motor? The highest pressure per horsepower is typically the rotary vane and highest flow per horsepower is going to be the fans. For environmental applications you see a lot of PD blowers and regenerative blowers being used because they fall in the middle as far and flow, pressure and horsepower required. Fans are used a lot on air stripper applications where high flow at low pressure is desired. Several other units that can be used for vacuum and pressure are the oil sealed liquid ring pump and the claw pump. These units can produce even higher pressure and vacuum than the units discussed above but are typically a lot more expensive. The liquid ring and claw pumps will be discussed in Part 5.
Noise can be a major factor of blower selection as well. None of these units are very quiet by themselves but silencers are available for most. In some cases sound blankets are place on interior walls of trailers or buildings in environmental applications to keep the neighbors from complaining about the noise. Fans do not do well with silencers as it can drastically change their performance. PD blowers and regenerative blowers work the best with silencers. Rotary vanes blowers can be silenced as well but it can reduce the performance substantially as well.
Blower units that produce the highest pressure typically produce the highest heat. Heat exchangers can be used to reduce the heat in air sparging applications or applications where the off gas will go through activated carbon. Heat is also a factor when the extracted vapor is explosive in the case of gasoline or methane gas. Special explosion proof versions of most of these blowers are available.
The last item I will discuss is durability. In my experience the regenerative blowers and PD blowers are the most durable and require the least amount of maintenance. The rotary vane blowers can require vane replacement every 4-6 months of operation. Some high end vane blowers such as Rietschle or Busch last a lot longer but cost quite a bit more. As with most things there are good brand names and cheap ones. I have had my best luck with Ametek (Rotron) regenerative blowers, NY or Lamson blower fans, Rietschle vane blowers and Roots Dressor PD blowers. It is unfortunate, but in a lot of cases the States Trust Funds dictate how much routine maintenance can be performed at a site. There are two reasons this is bad. First, the amount of maintenance allowed (or paid for) is way less than recommended by the equipment manufacturers. Therefore, the equipment does not last as long. Second, a good majority of the time, the maintenance is performed or attempted by persons not trained to do this type of work. This problem is not as prevalent on the Federal, Military or larger industrial site because the regulators are not controlling the purse strings.